1. Technical Field
The present invention relates to a liquid drop expelling head which expels liquid drops, and to an image forming device provided with the liquid drop expelling head.
2. Related Art
Among liquid drop expelling heads of inkjet recording devices (hereinafter called “image forming devices”), there are those which impart vibration to the meniscus of the ink at the nozzle in order to prevent the ink from thickening (Japanese Patent Application Laid-Open (JP-A) No. 9-201960).
At times of liquid drop expulsion standby when a liquid drop is not being expelled from the nozzle, vibration is imparted intermittently to the meniscus of the nozzle to the extent that a liquid drop is not expelled therefrom. Further, vibration is continuously imparted to the meniscus immediately before printing begins.
In this way, by imparting vibration intermittently at the time of liquid drop expulsion standby and imparting vibration continuously before printing starts, fatigue and noise of the driving element are reduced, thickening of the ink is prevented, and clogging of the nozzle is prevented.
However, at this liquid drop expelling head, there is merely the structure of always applying the same vibration before printing starts, regardless of the extent of thickening of the ink or the expelling conditions of the ink drop to be expelled. Therefore, there are cases in which the effects of imparting vibration are insufficient, and cases in which, oppositely, the effects of imparting vibration are excessive.
In cases in which the effects of imparting vibration are insufficient, thickening of the meniscus surface progresses, and the problem arises that the expulsion speed of the first drop at the time of starting expulsion again is greatly reduced. However, in this case, because the thickened ink is removed due to the expulsion of the first drop, the expulsion speeds of the drops from the second drop on are hardly reduced at all.
On the other hand, in cases in which the effects of imparting vibration are excessive, the thickened ink is excessively dispersed within the ink flow path. Therefore, although the amount of reduction of the expulsion speed of the of the first drop is kept to a minimum, the dispersed thickened ink cannot be removed only in that first drop, and thus, there is the problem that the expulsion speeds of the ink drops from the second drop on as well are reduced.
In this way, problems arise both when the effects of meniscus vibration applied at times of expulsion standby are insufficient and when they are excessive.